The three-step synthesis of new, air-stable, PNN′O-tetradentate ligands 3a·HH–3c·HH by Schiff base condensation of the 1° amines 2a–2c with 2-Ph2PC6H4(CHO) in refluxing EtOH is described. The racemic ligand 3d·HH, isolated in 79% yield, was successfully prepared from 2-C6H4(OH){C(O)NHCH2CH(Me)NH2} 2d and 2-Ph2PC6H4(CHO) in absolute EtOH. Upon careful choice of metal precursor, ligands 3a·HH–3d·HH display various coordination modes. Reaction of 3a·HH with AuCl(tht) (1:1 molar ratio) affords AuCl(3a·HH), 4a, in which κ1-P-complexation of the functionalised ligand is observed. In contrast, reaction of 3a·HH (or 3d·HH) with MCl2(cod) (M = Pt, Pd) affords MCl2(3a·HH) (M = Pt, 5a; M = Pd, 5b) or MCl2(3d·HH) (M = Pt, 5c; M = Pd, 5d) in which ligand chelation is achieved using both P and imine N donor atoms. Moreover κ2-P,N-chelation was also observed when 3a·HH–3c·HH were separately allowed to react with [PdCl(η3-C3H5)]2 in CH2Cl2 affording new cationic η3-allyl complexes [Pd(η3-C3H5)(3a·HH–3c·HH)]Cl, 6a–6c. Two neutral (methyl)chloropalladium(II) complexes, 7a/7c, were isolated in high yields from 3a·HH or 3c·HH and Pd(CH3)Cl(cod). Elimination of cod and single methyl protonation from Pt(CH3)2(cod) with 1 equiv. of 3a·HH, 3b·HH or 3d·HH in toluene, at room temperature, afforded square-planar complexes Pt(CH3)(κ3-3a·H/3b·H/3d·H), 8a/8b/8d, containing monoanionic κ3-PNN′-tridentate ligands. The κ3-PNN′-tridentate mode was likewise observed for Pd(CH3)(3a·H/3c·H), 10a/10c, upon treatment of a methanolic solution of Pd(CH3)Cl(3a·HH/3c·HH) with tBuOK. Similarly the monohapto (allyl)PdII compounds Pd(CH2CHCH2)(3a·HH–3c·HH), 9a–9c, were obtained cleanly from 6a–6c and tBuOK via an η3→η1 allyl isomerisation. Both amide and phenolic protons in 5a–5d were smoothly deprotonated, with base, to give the κ4-PNN′O-tetradentate complexes 11a/11b and 11d/11e containing the dianionic ligands 3a2−/3d2− respectively. The NiII complexes 11c and 11f were synthesised directly from NiCl2·6H2O, 3a·HH (or 3d·HH) and tBuOK in CH3OH. All new compounds were characterised by multinuclear NMR, FT–IR, mass spectrometry and microanalysis. Single crystal X-ray studies have been undertaken on the compounds 3a·HH, 3c·HH, 4a, 7c, 8a, 8b, 8d and 11a–11d.

The three-step synthesis of new, air-stable, PNN′O-tetradentate ligands 3a·HH–3c·HH by Schiff base condensation of the 1° amines 2a–2c with 2-Ph2PC6H4(CHO) in refluxing EtOH is described. The racemic ligand 3d·HH, isolated in 79% yield, was successfully prepared from 2-C6H4(OH){C(O)NHCH2CH(Me)NH2} 2d and 2-Ph2PC6H4(CHO) in absolute EtOH. Upon careful choice of metal precursor, ligands 3a·HH–3d·HH display various coordination modes. Reaction of 3a·HH with AuCl(tht) (1:1 molar ratio) affords AuCl(3a·HH), 4a, in which κ1-P-complexation of the functionalised ligand is observed. In contrast, reaction of 3a·HH (or 3d·HH) with MCl2(cod) (M = Pt, Pd) affords MCl2(3a·HH) (M = Pt, 5a; M = Pd, 5b) or MCl2(3d·HH) (M = Pt, 5c; M = Pd, 5d) in which ligand chelation is achieved using both P and imine N donor atoms. Moreover κ2-P,N-chelation was also observed when 3a·HH–3c·HH were separately allowed to react with [PdCl(η3-C3H5)]2 in CH2Cl2 affording new cationic η3-allyl complexes [Pd(η3-C3H5)(3a·HH–3c·HH)]Cl, 6a–6c. Two neutral (methyl)chloropalladium(II) complexes, 7a/7c, were isolated in high yields from 3a·HH or 3c·HH and Pd(CH3)Cl(cod). Elimination of cod and single methyl protonation from Pt(CH3)2(cod) with 1 equiv. of 3a·HH, 3b·HH or 3d·HH in toluene, at room temperature, afforded square-planar complexes Pt(CH3)(κ3-3a·H/3b·H/3d·H), 8a/8b/8d, containing monoanionic κ3-PNN′-tridentate ligands. The κ3-PNN′-tridentate mode was likewise observed for Pd(CH3)(3a·H/3c·H), 10a/10c, upon treatment of a methanolic solution of Pd(CH3)Cl(3a·HH/3c·HH) with tBuOK. Similarly the monohapto (allyl)PdII compounds Pd(CH2CHCH2)(3a·HH–3c·HH), 9a–9c, were obtained cleanly from 6a–6c and tBuOK via an η3→η1 allyl isomerisation. Both amide and phenolic protons in 5a–5d were smoothly deprotonated, with base, to give the κ4-PNN′O-tetradentate complexes 11a/11b and 11d/11e containing the dianionic ligands 3a2−/3d2− respectively. The NiII complexes 11c and 11f were synthesised directly from NiCl2·6H2O, 3a·HH (or 3d·HH) and tBuOK in CH3OH. All new compounds were characterised by multinuclear NMR, FT–IR, mass spectrometry and microanalysis. Single crystal X-ray studies have been undertaken on the compounds 3a·HH, 3c·HH, 4a, 7c, 8a, 8b, 8d and 11a–11d.

The synthesis, structural characterization, and magnetic properties of four related heterometallic complexes with formulas [DyIII2CoII(C7H5O2)8]·6H2O (1), [DyIII2NiII(C7H5O2)8]·(C7H6O2)2 (2), TbIII2CoII(C7H5O2)8 (3), and DyIII2CdII(C7H5O2)8 (4) were reported. Each of complexes has a perfectly linear arrangement of the metal ions with two terminal LnIII (LnIII = DyIII, TbIII) ions and one central MII (MII = CoII, NiII, CdII) ion. It was found that 1–3 displayed obvious magnetic interactions between the spin carriers according to the direct current (dc) susceptibility measurements. Alternating current (ac) magnetic susceptibility measurements indicate that complexes 1–4 all exhibit single-molecule magnet (SMM) behavior, while the replacement of the diamagnetic CdII by paramagnetic ions leads to a significant slowing of the relaxation thanks to the magnetic interactions between 3d and 4f ions, resulting in higher relaxation barrier for complexes 1 and 2. Moreover, both Dy2Co and Dy2Ni compounds exhibit dual relaxation pathways that may originate from the single ion behavior of individual DyIII ions and the coupling between DyIII and CoII/NiII ions, respectively, which can be taken as the feature of 3d–4f SMMs. The Ueff for 1 of 127 K is a relatively high value among the reported 3d–4f SMMs. The results demonstrate that the magnetic coupling between 3d and 4f ions is crucial to optimize SMM parameters. The synthetic approach illustrated in this work represents an efficient route to design nd–4f based SMMs via incorporating suitable paramagnetic 3d and even 4d and 5d ions into the d–f system.

The reaction of Mn(OAc)2·4H2O and Ln(NO3)3·6H2O with N-(2-aminopropyl)-2-hydroxybenzamide and salicylic aldehyde in methanol/methylene dichloride produces yellow crystals of Ln2Mn(C7H5O2)8 (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)), in the presence of triethylamine. Three metal ions are connected by six μ2-phenolate oxygen atoms of six salicylic aldehyde ligands, resulting in perfect linear [LnIII–MnII–LnIII] structures. Magnetic studies of these complexes have been performed and AC susceptibility measurements show the presence of a temperature-dependent out-of-phase ac signal for complexes 2 and 3 indicating single-molecule magnet (SMM) behavior. The DyIII2MnII compound shows double relaxation pathways which may originate from the single ion behavior of individual DyIII ions and the weak coupling between DyIII and MnII ions, respectively. The Ueff of 92.4(2) K is a relatively high value among 3d–4f SMMs. Moreover, complexes 2 and 3 represent the first linear Mn–Ln SMMs containing only divalent manganese ions as far as we know. The result suggests the positive effects of magnetic coupling to enhance their SMM behavior, presenting a promising strategy for constructing efficient heterometallic SMMs.

The reaction of Mn(OAc)2·4H2O and Ln(NO3)3·6H2O with N-(2-aminopropyl)-2-hydroxybenzamide and salicylic aldehyde in methanol/methylene dichloride produces yellow crystals of Ln2Mn(C7H5O2)8 (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)), in the presence of triethylamine. Three metal ions are connected by six μ2-phenolate oxygen atoms of six salicylic aldehyde ligands, resulting in perfect linear [LnIII–MnII–LnIII] structures. Magnetic studies of these complexes have been performed and AC susceptibility measurements show the presence of a temperature-dependent out-of-phase ac signal for complexes 2 and 3 indicating single-molecule magnet (SMM) behavior. The DyIII2MnII compound shows double relaxation pathways which may originate from the single ion behavior of individual DyIII ions and the weak coupling between DyIII and MnII ions, respectively. The Ueff of 92.4(2) K is a relatively high value among 3d–4f SMMs. Moreover, complexes 2 and 3 represent the first linear Mn–Ln SMMs containing only divalent manganese ions as far as we know. The result suggests the positive effects of magnetic coupling to enhance their SMM behavior, presenting a promising strategy for constructing efficient heterometallic SMMs.